Rudimentary means what did not develop or improved. It's something found in the initial stage, elementary.
Rudimentary is an adjective referring to rudiment – initial element, beginning, first notions. It is a general and superficial knowledge of an art or science.
In natural history, rudimentary refers to an organ that has not developed to perfection.
rudimentary agriculture
Rudimentary agriculture refers to an underdeveloped agriculture, practiced using rudimentary, precarious resources. A typical example of rudimentary agriculture was used in the first period of feudalism – a fundamentally agrarian system – where human strength was intensely used and exploited.
In feudalism, the rhythm of work on the land marked the daily life of the serf. Rudimentary techniques made this daily life extremely arduous and production was low, producing only what was necessary for the consumption of the manor. Only with the growth of population and trade would new planting techniques be introduced.